Btrfs: don't access non-existent key when csum tree is empty
When the csum tree is empty, our leaf (path->nodes[0]) has a number of items equal to 0 and since btrfs_header_nritems() returns an unsigned integer (and so is our local nritems variable) the following comparison always evaluates to false: if (path->slots[0] >= nritems - 1) { As the casting rules lead to: if ((u32)0 >= (u32)4294967295) { This makes us access key at slot paths->slots[0] + 1 (1) of the empty leaf some lines below: btrfs_item_key_to_cpu(path->nodes[0], &found_key, slot); if (found_key.objectid != BTRFS_EXTENT_CSUM_OBJECTID || found_key.type != BTRFS_EXTENT_CSUM_KEY) { found_next = 1; goto insert; } So just don't access such non-existent slot and don't set found_next to 1 when the tree is empty. It's very unlikely we'll get a random key with the objectid and type values above, which is where we could go into trouble. If nritems is 0, just set found_next to 1 anyway as it will make us insert a csum item covering our whole extent (or the whole leaf) when the tree is empty. Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com> Signed-off-by: Chris Mason <clm@fb.com>
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@ -750,7 +750,7 @@ again:
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int slot = path->slots[0] + 1;
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int slot = path->slots[0] + 1;
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/* we didn't find a csum item, insert one */
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/* we didn't find a csum item, insert one */
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nritems = btrfs_header_nritems(path->nodes[0]);
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nritems = btrfs_header_nritems(path->nodes[0]);
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if (path->slots[0] >= nritems - 1) {
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if (!nritems || (path->slots[0] >= nritems - 1)) {
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ret = btrfs_next_leaf(root, path);
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ret = btrfs_next_leaf(root, path);
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if (ret == 1)
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if (ret == 1)
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found_next = 1;
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found_next = 1;
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